Air quality is crucial to life, and many companies are researching filtration materials for removing airborne contaminants, such as particulates and volatile organic compounds (VOC), with high efficiency and low air-flow resistance. The development of fibrous air filtration materials has recently focused on use of super fine fibers (e.g. nanofibers) or charged fibers to trap contaminants presented in an air stream. Use of nanofibers generally causes a relatively large pressure drop or air-flow resistance, which may have adverse effects in some air filtration applications. On the other hand, the adsorption ability of charged fibers is limited by the amount of such fibers in the fibrous web, and the effectiveness of charged fibers to adsorb airborne particulates is limited and diminishes over time as these materials reach their charge saturation limits. Furthermore, the use of such fibers alone generally cannot effectively eliminate odors due, for example, to the presence of VOC, such as formaldehyde and the like.
U.S. Pat. Nos. 5,230,800 and 5,792,242; and EP Patent No. 0881931B1 disclose filters incorporating electrostatically-charged fibers. Some recent patents describe use of photo-catalytic particulates (e.g. titanium dioxide) or photo-catalytic fibers to reduce odors. CN 101428209A discloses a titanium dioxide catalyst supported on a nanofiber prepared by electrospinning. CN 1593766A discloses an aluminum honeycomb photocatalyst filter prepared by spray coating.